Food Intolerance Glossary

This glossary defines the terms you meet most often when you are trying to work out which foods upset you. Each entry leads with a plain definition, names the authority behind it, and points you to a fuller page. Some of these terms are well established. Others are contested or have no single validated test, and we say so plainly. Food intolerance is a busy field with a lot of confident marketing, so we keep the certainty honest: a pattern in your own logs is a suspect worth testing, not a verdict.

Conditions

Food intolerance

Food intolerance is a non-allergic, non-immune reaction to a food or food component, often involving difficulty digesting or processing it (for example lactose). It is different from a food allergy, which involves the immune system and can be life threatening; intolerance reactions are usually dose-related and not life threatening. The NHS notes that intolerance symptoms are often slower to appear and tied to how much you eat (NHS, Food intolerance).

Food sensitivity

Food sensitivity is a loose, non-clinical umbrella term people use for unpleasant but non-allergic reactions to food, often used interchangeably with food intolerance. It is not a formal diagnostic category, and there is no single validated test that confirms a "food sensitivity," so the term means different things to different people. Major allergy bodies stress that IgG food-sensitivity blood panels are not a reliable way to identify problem foods (AAAAI, JACI 2010).

Food allergy

A food allergy is an immune-system reaction, most often involving IgE antibodies, that occurs reproducibly on exposure to a specific food and can range from mild to life threatening (anaphylaxis). It is not the same as food intolerance: an allergy is an immune response and can be triggered by tiny amounts, whereas intolerance is usually dose-related and not life threatening. The WHO and allergy bodies define food allergy by this reproducible, immune-mediated mechanism (NHS, Food allergy).

Histamine intolerance

Histamine intolerance is a proposed condition in which symptoms (such as flushing, headache, hives, or gut upset) are thought to follow eating histamine-rich foods, possibly linked to reduced activity of the enzyme that breaks histamine down. It is contested: there is no single validated diagnostic test, the evidence base is limited, and diagnosis rests largely on symptom patterns and dietary response. EFSA has reviewed histamine in food and the difficulty of setting clear individual thresholds (EFSA, Scientific Opinion on biogenic amines).

MCAS (mast cell activation syndrome)

MCAS is a condition in which mast cells release their chemical mediators (including histamine) inappropriately or excessively, producing recurrent symptoms across multiple body systems. It is genuinely contested at its edges: diagnostic criteria are debated, and the strict ("consensus-1") criteria require objective evidence such as a rise in serum tryptase during an episode, not symptoms alone. A low-histamine diet may help some people but is not a diagnosis (AAAAI, mast cell disorders).

Mastocytosis

Mastocytosis is a rare disorder in which abnormal mast cells accumulate in the skin, bone marrow, or other organs, sometimes causing flushing, itching, and reactions to triggers. It is a distinct, diagnosable disease (often involving specific mutations and raised baseline tryptase), and it is not the same as MCAS, though they can overlap. It is diagnosed and managed by specialists (NHS, Mastocytosis).

SIBO (small intestinal bacterial overgrowth)

SIBO is a condition in which an abnormally large or abnormal type of bacteria grows in the small intestine, which can cause bloating, gas, diarrhea, and discomfort. It is usually assessed with a breath test, and its definition and testing remain debated among specialists. It overlaps with IBS symptoms but is a separate concept (Cleveland Clinic, SIBO).

IBS (irritable bowel syndrome)

IBS is a common, long-term functional gut disorder defined by recurrent abdominal pain with changes in bowel habit, without structural damage that explains it. It is a recognized diagnosis made on symptom criteria after ruling out other causes, not a "non-disease," and diet (including a low-FODMAP approach) is one management option. NICE provides clinical guidance on diagnosis and management (NICE, IBS in adults).

FODMAP

FODMAPs are a group of fermentable short-chain carbohydrates (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols) that can be poorly absorbed and trigger gut symptoms in sensitive people. The term names the food chemicals, not a disease; the low-FODMAP diet is a structured, time-limited approach developed and maintained by Monash University (Monash University, FODMAP).

Lactose intolerance

Lactose intolerance is a condition in which the body produces too little lactase, the enzyme that digests the milk sugar lactose, leading to bloating, gas, and diarrhea after dairy. It is dose-related: many people can handle small amounts, and it is an intolerance, not a milk allergy. The NHS describes the symptoms and dietary management (NHS, Lactose intolerance).

Fructose malabsorption

Fructose malabsorption is a condition in which the small intestine does not absorb fructose well, so unabsorbed fructose ferments in the gut and causes bloating, gas, and diarrhea. It is not the same as hereditary fructose intolerance, a rare genetic disorder that is serious and managed medically. It is one of the FODMAP-related sugars addressed in the Monash framework (Monash University, FODMAP).

Related: Fructose malabsorption, FODMAP

Gluten intolerance / NCGS (non-celiac gluten sensitivity)

NCGS is a proposed condition in which people report gut and other symptoms after eating gluten or wheat, despite testing negative for celiac disease and wheat allergy. It is contested: there is no validated biomarker or single test, diagnosis is made by exclusion and symptom response, and some research points to other wheat components rather than gluten itself. Coeliac UK explains the distinction from celiac disease (Coeliac UK, gluten sensitivity).

Celiac disease

Celiac disease is an autoimmune condition in which eating gluten triggers the immune system to damage the lining of the small intestine. It is a diagnosable disease (confirmed with specific blood tests and usually a biopsy, while still eating gluten), not an intolerance or a lifestyle choice, and the only current management is a strict lifelong gluten-free diet. Coeliac UK and the NHS describe diagnosis and management (NHS, Coeliac disease).

Salicylate sensitivity

Salicylate sensitivity is a proposed intolerance to salicylates, natural chemicals found in many fruits, vegetables, spices, and some medicines, reported to cause symptoms such as hives, gut upset, or breathing changes. It is contested: there is no validated blood test, diagnosis relies on supervised elimination and reintroduction, and reactions are thought to be dose-related rather than allergic. The salicylate elimination framework is associated with the RPAH (Royal Prince Alfred Hospital) elimination diet (RPAH Allergy Unit).

Sulfite sensitivity

Sulfite sensitivity is a reaction to sulfites, preservatives used in some wines, dried fruit, and processed foods, which can cause symptoms such as wheezing, especially in some people with asthma. It is recognized enough that sulfites above a set level must be declared on food labels, though it is usually an intolerance-type reaction rather than a classic allergy. Sulfites are regulated food additives (EFSA, sulfites re-evaluation), and they can trigger airway reactions such as wheezing, chest tightness, or an asthma flare in some people, especially those with asthma (Allergy UK, sulphites and airway symptoms).

Tyramine sensitivity

Tyramine sensitivity is a reaction to tyramine, a biogenic amine found in aged, fermented, and cured foods (such as aged cheese, cured meat, and some fermented products), most often reported as a headache or migraine trigger. It matters most for people taking MAOI medicines, where tyramine-rich foods can cause a dangerous blood-pressure rise. The interaction between tyramine and MAOIs is well documented in pharmacology references (Cleveland Clinic, MAOIs).

Oxalate

Oxalate (oxalic acid) is a natural compound found in many plant foods (such as spinach, rhubarb, and nuts) that can bind calcium and, in some people, contribute to kidney stones. A low-oxalate diet is mainly used for people who form calcium-oxalate kidney stones; broad "oxalate sensitivity" as a cause of general symptoms is not well established. The National Kidney Foundation describes the oxalate-stone link (National Kidney Foundation).

Related: Oxalate, Food intolerance

Nightshade sensitivity

Nightshade sensitivity is a reported intolerance to plants in the nightshade (Solanaceae) family, such as tomatoes, peppers, potatoes, and aubergine, blamed by some people for joint or gut symptoms. It is not an established clinical diagnosis: there is no validated test, and evidence that nightshades worsen conditions like arthritis in the general population is weak. Reactions, where real, are individual and best assessed by careful elimination and reintroduction (British Dietetic Association).

Caffeine sensitivity

Caffeine sensitivity describes a heightened response to caffeine, where smaller amounts cause symptoms such as jitteriness, palpitations, anxiety, or sleep disruption, partly influenced by genetics and how quickly a person metabolizes caffeine. It is dose-related and individual, not an allergy, and it is influenced by tolerance and other stimulants. The EFSA has published safe-intake guidance for caffeine in the general population (EFSA, caffeine safety).

Mechanisms and methods

DAO (diamine oxidase)

DAO is an enzyme, found mainly in the gut lining, that breaks down histamine from food before it enters the bloodstream. Reduced DAO activity is the main mechanism proposed behind histamine intolerance, though measuring DAO is not a validated stand-alone diagnostic test for it. The role of DAO in histamine metabolism is described in reviews on biogenic amines (SIGHI, histamine intolerance).

Mast cell

A mast cell is a type of immune cell that stores and releases chemical mediators, including histamine, as part of allergic and inflammatory responses. When mast cells release these mediators inappropriately, they are central to conditions such as mastocytosis and the proposed MCAS. Their role is described by allergy and immunology bodies (AAAAI, mast cells).

IgE

IgE (immunoglobulin E) is a type of antibody the immune system makes that drives classic, immediate allergic reactions, including food allergy and anaphylaxis. A raised IgE to a specific food can support an allergy diagnosis when interpreted with the clinical history, but it is not used to diagnose food intolerance. Allergy bodies describe IgE testing and its limits (BSACI, allergy testing).

IgG / IgG4

IgG and its subclass IgG4 are antibodies that the immune system commonly produces after exposure to foods, and they are the basis of many commercial "food sensitivity" panels. Major allergy organizations advise against using IgG or IgG4 food panels to diagnose food allergy or intolerance: a positive result more likely reflects normal exposure and tolerance than a problem food. The EAACI, AAAAI, and BSACI have all issued statements against their diagnostic use (EAACI, position on IgG4 testing).

Histamine

Histamine is a chemical messenger involved in immune responses, stomach acid, and nerve signaling, and it is also present in many fermented and aged foods. High intake from food, combined with reduced breakdown, is the proposed mechanism behind histamine-related symptoms in some people, though individual thresholds are hard to define. EFSA has assessed histamine in foods (EFSA, biogenic amines).

Biogenic amines

Biogenic amines are nitrogen compounds (including histamine, tyramine, and putrescine) formed mainly when bacteria break down proteins during fermentation, ageing, or spoilage. They are the food chemicals behind several intolerance-type and migraine-type reactions, and their levels rise as foods ferment or age. EFSA has reviewed the food-safety aspects of biogenic amines (EFSA, biogenic amines).

Elimination diet

An elimination diet is a structured method in which suspected foods are removed for a set period to see whether symptoms improve, before they are reintroduced. It is a diagnostic and management tool, ideally done with support from a dietitian, not a long-term way of eating, because over-restriction carries its own risks. The British Dietetic Association advises professional supervision for elimination diets (British Dietetic Association).

Reintroduction

Reintroduction is the controlled step of adding a removed food back into the diet, one at a time, to check whether symptoms return and to confirm or clear that food. It is the part of an elimination process that actually gives information, because removal alone cannot tell you what is safe. Dietetic guidance treats reintroduction as essential to avoid unnecessary long-term restriction (British Dietetic Association).

Delayed (non-IgE) reaction

A delayed or non-IgE reaction is a response to a food that appears hours or even a day or more after eating, rather than within minutes. Because the delay breaks the obvious cause-and-effect link, these reactions are hard to pin to a single meal and are easy to misattribute. Allergy bodies recognize non-IgE-mediated food reactions as distinct from immediate IgE allergy (NICE / BSACI guidance on non-IgE food allergy).

Dose / threshold ("the bucket")

Dose or threshold is the idea that many intolerance reactions depend on how much of a trigger builds up, so a small amount may be fine while a larger or repeated amount tips you over. "The bucket" is the common metaphor: symptoms appear when total load (across foods, and sometimes other factors) overflows your personal limit. This dose-related pattern is a defining feature of intolerance, as opposed to allergy, in NHS descriptions (NHS, Food intolerance).

Case-crossover method

The case-crossover method is a study design that compares a person's exposures shortly before a symptom episode with their own exposures during symptom-free periods, using each person as their own control. It is useful for spiky, intermittent problems and reduces some between-person confounding, but a correlation it surfaces is still a suspect to test, not proof of cause. The design is established in epidemiology for studying transient triggers (Maclure, case-crossover design, Am J Epidemiol 1991, PMID 1985444).

Related: Delayed (non-IgE) reaction

Tryptase

Tryptase is an enzyme released by mast cells, and its level in the blood is used as a marker of mast cell activity. A rise in serum tryptase during a reaction is part of the strict criteria for mast cell activation, and a persistently high baseline level can point toward mastocytosis. Allergy and immunology bodies describe tryptase testing in mast cell disorders (AAAAI, mast cell disorders).

Antihistamine

An antihistamine is a medicine that blocks the action of histamine at its receptors, used to ease symptoms such as itching, hives, and some allergy and reaction symptoms. It can reduce symptoms but does not diagnose their cause, and any use, including around suspected food reactions, should be discussed with a clinician or pharmacist. The NHS describes how antihistamines work and their uses (NHS, Antihistamines).

Scombroid (histamine) poisoning

Scombroid poisoning is a food-borne illness caused by eating fish that has spoiled and built up high levels of histamine, producing flushing, headache, and rash that mimic an allergic reaction. It is a poisoning from the food itself, not a personal intolerance or allergy, and it can affect anyone who eats the affected fish. The CDC and FDA describe scombroid (histamine fish poisoning) (CDC, scombroid poisoning).

n-of-1

An n-of-1 study is a structured single-person experiment in which one individual is observed across different conditions (such as eating and avoiding a food) to look for patterns in their own data. It can reveal a pattern that is real for that one person, but it is never a population fact, and a correlation it shows is a suspect to test, not proof of cause. The n-of-1 design is recognized in evidence-based medicine for individual-level questions (Gabler et al., n-of-1 trials systematic review, Med Care 2011, PMID 21478771).

Related: Elimination diet

A note on the contested terms

Several terms here (histamine intolerance, MCAS, non-celiac gluten sensitivity, "food sensitivity," salicylate and nightshade sensitivity) are real experiences for many people but remain contested in the literature, with no single validated test. That does not mean your symptoms are not real. It means the science is still working out the mechanisms, and that a careful pattern in your own data is a starting point for investigation with a clinician, not a final answer. Correlation is not cause.

Health disclaimer

GIMETRY is not a medical device and does not provide medical advice, diagnosis, or treatment. This glossary is for general information only. Always consult a qualified clinician or registered dietitian about your symptoms, before starting an elimination diet, or before changing how you eat or take medicines.

How this was written

AI-assisted, human-reviewed through the GIMETRY editorial process. Last reviewed 2026-06-28. GIMETRY is not a medical device. Definitions are drawn from named public-health and specialist authorities, cited inline.